1. Field of the invention
The present invention is generally concerned with filters employed to clean a fluid circulating in a pressurized network and likely to entrain debris, detritus or foreign bodies.
This is the case, for example, with industrial effluent which can entrain debris or detritus of man-made origin or vegetable matter, for example algae of a more or less fibrous or filamentary nature, or animals such as mussels, molluscs or fish, likely to proliferate on the downstream side if not previously separated out.
2. Description of the prior art
The filters employed to clean such industrial effluent have in practise to be inserted into the pipe carrying same and they generally comprise, in a filter body adapted to be connected to two consecutive sections of a pipe, a filter member designed to be inserted into the flow to be treated and itself comprising a filter element having openings adapted to allow free circulation of the liquid whereas its solid parts are adapted to hold back debris, detritus or foreign bodies carried in the liquid.
The present invention is more particularly directed to the case where, to obtain a so-called self-cleaning filter, provision is made for systematically eliminating such debris, detritus and foreign bodies.
The direction of flow is systematically reversed at approporiate times in some installations which, ignoring internal valves necessary for their functioning, have the advantage of having virtually no moving parts.
However, this entails taking temporarily out of service either the filter as a whole or at least one section of the filter, to the detriment of overall efficiency.
In other installations which have no moving parts at all, the required elimination of debris, detritus and foreign bodies held back by the filter member is very simply obtained by construction features whereby the incoming flow washes over the filter element.
If the filter member comprises a cylindrical screen as the filter element, for example, the filter body is disposed around the screen spiral staircase-fashion and the flow to be treated enters the filter body tangentially so that the speed vector of the incoming flow is oblique to the surface of the screen and thus has not only a component perpendicular to its surface, necessary for the flow to pass through it, but also a tangential component by virtue of which the debris, detritus and foreign bodies that are held back are systematically entrained.
Although satisfactory in other respects, these installations are mostly relatively bulky and require a change in the direction of the flow to be treated because although the flow enters tangentially it necessarily leaves axially, which means that they are sometimes difficult to install, especially in existing installations, with the result that they do not suit all applications.
In other installations a mechanical cleaning device is used to achieve the required self-cleaning function.
At present, the filter member usually employs as the filter element a fixed part-cylindrical screen near which is a counterflow (i.e. on the upstream side relative to the corresponding flow) suction unit which discharges to a drain via a take-off pipe and which is rotatable about the axis of the filter member.
One disadvantage of such installations using a mechanical cleaning device is that they give rise to non-negligible head losses.
A general object of the present invention is an arrangement whereby these disadvantages can be minimized or even eliminated.